Scleraxis-expressing progenitor cells are critical for the maturation of the annulus fibrosus and demonstrate therapeutic potential.

BACKGROUND

Annulus fibrosus (AF) is an important part of the intervertebral disc (IVD) and its injury leads to back pain and impaired mobility. The stem/progenitor cells are essential for the maturation and repair of the AF, however, the identity of AF stem/progenitor cells remain elusive.

METHODS

In this study, we sorted cells from the murine IVDs and performed the single-cell RNA sequencing. Using single-cell transcriptomics, genetic lineage tracing, in vitro stem cell experiment, ablation models and cell transplantation, we elucidate the role of AF progenitor cells in maturation and injury.

RESULTS

On the basis of single-cell RNA-sequencing (scRNA-seq) analysis of the intervertebral disc, we found that the transcription factor Scleraxis (Scx) can specifically label a progenitor cell population of the outer AF. By lineage tracing assay, Scx-lineage AF cells proliferate mainly prior to sexual maturity, but barely proliferate after age of 8 weeks. The Scx-expressing AF cells are enriched for stem/progenitor cell markers and show a higher proliferative capacity and differentiation potential than the Scx - cells. The ablation of Scx-expressing AF cells impairs the maturation of AF. The Scx + AF cells are enriched for TGFβ signaling. Transplantation of Scx-lineage cells to injured AF with Connective tissue growth factor (CTGF) improved the AF healing.

CONCLUSIONS

Scleraxis-expressing progenitor cells are critical for the maturation of AF and demonstrate therapeutic potential for AF regeneration.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: These findings expand the important role of stem cells in maturation and repair and provide new strategy for cellular therapy of AF repair.